1. Field of the Invention
The present invention relates to a surface illuminator for illuminating, for example, a liquid crystal display panel from the back of the panel.
2. Description of the Prior Art
FIG. 1 is a perspective view of a conventional surface illuminator which is disclosed, for example, in Japanese Utility Model Laid Open No. 69281/87. In the same figure, the reference numeral 1 denotes a light guide plate; numerals 2a and 2b denote incandescent lamps disposed at an end face of the light guide plate 1; and numeral 3 denotes a reflection frame which surrounds the light guide plate 1 and the incandescent lamps 2a, 2b.
The operation of such conventional surface illuminator will now be described. Light rays from the incandescent lamps 2a and 2b are conducted as in FIG. 2 by the light guide plate 1. At this time, the light rays are scattered and reflected by a scattering/reflection layer (not shown) formed on the back of the light guide plate 1, then are radiated from the surface of the light guide plate, whereby a liquid crystal display panel (not shown) or the like disposed on the front face of the light guide plate 1 can be illuminated.
The conventional surface illuminator is constructed as above, so for example, in the case where the incandescent lamp 2a is disposed so that a longitudinal direction of a filament 2c of the lamp 2a is parallel to an end face la of the light guide plate 1, as shown in FIG. 3, a luminance distribution of the incandescent lamp 2a is as indicated by dotted line A (the light intensity is uniform on the dotted line). That is, the portion of the end face la of the light guide plate 1 close to the incandescent lamp 2a is large in the amount of incident light, while the portion thereof far from the lamp 2a is small in the amount of incident light. After all, there is obtained such an incident light volume distribution as indicated by dotted line B, thus causing the problem of localization.
As shown in FIG. 2, moreover, light rays emitted from the incandescent lamps 2a, 2b and having an angle of incidence not smaller than a critical angle of the light guide plate 1 (about 45.degree. in the case of an acrylic light guide plate) are reflected without entering the interior of the light guide plate, with the result that the light radiated from the surface of the light guide plate is strong at the portion close to the incandescent lamps 2a, 2b and weak at the portion far from the lamps, thus making it impossible to obtain a uniform surface illumination.